Compressor unloader



S. B. REDFIELD.

COMPRESSOR UNLOADER.

APPLICATION FlLED AUG.5.192|.

Patented Sept. 12, 1922.

INVENTOR izoufamoqfle ZT-:

H15 ATTO NEY Patented Sept, l2, i922 mrao SNOWDEN B. REDFIELD, OF EASTON, EENNSYLVANIA, ASSIGNOR TO INGERSOLL-RAND COMPANY, 0F JERSEY CITY, yN'EVV JERSEY, A CORPORATION 0F NEW JERSEY.

COMFRESSOR 'UNLOADER- Application led August 15, 1921. Serial No. 492,568.

T 0 all whom it may cof/cern Be it known that, I, SNowDEN B. RED- FIELD, a citizen of the United States, and a4 resident of Easton, Northampton County, State of Pennsylvania, have invented a certain Compressor Unloader, of which the following is .a specification, accompanied by drawings rlhis invention relates to compressor unloaders but more particularly to an unloader for relieving the fluid compression load during the period of starting. The compressor may be operated for instance by an electric motor automatically started and stopped by means of an automatic pressure controlled electric switch, while my unloader has no connection with the control switch and the unloading and loading operations are performed only by the action of the compressor itself.A`

rlhe invent-ion is in some respects an improvement upon the unloader disclosed in my former patent No. 1,421,309 granted June 27, 1922, and the objects of the invention are to simplify the apparatus and obtain quicker unloading, even before complete stoppage of the machine.

Further objects of the invention will hereinafter appear and to all of these ends the invention is shown in the accompanying drawings in which Figure 1 is a longitudinal sec-tional ele vation of the unloader, and' Figure 2 is a diagrammatic elevation partly in vertical section of the .unloader applied to a compressor unit.

Referring to the drawings and at first to Figure 2. the unloader A is connected in the discharge line B of a compressor@ between the compressor and the usual receiver D. rlhe compressor, shown diagrammatically for simplicity, comprises the cylinder E having the reciprocating piston F adapted to be driven from any suitable source of power as an electric motor (not shown). The compressor is provided with the inlet valves G and discharge valves H, and the discharge chamber J is connected to the discharge line B.

The unloader shown in detail in Figure 1 comprises the valve casing K having the main valve chamber L separated from the outlet 0 by a partition Pon which the main check valve Q is adapted to be seated for controlling the discharge from thel casing.

rlhe check valve Q is provided with a the cap S, which cap also forms a valve guide. The pressure in the receiver tank D normally holds the main check valve Q to its seat.

The wall T of the casing K is provided with a valve seat U on which a relief valve V is adapted to be seated, for controlling communication between the main valve chamber L and an atmospheric relief port X conveniently located in the sidev of the extension Y of the main casing K in which the relief valve V operates. The relief valve V is preferably carried by a piston Z and has limited longitudinal movement relatively to the piston, being urged inwardly by a comparatively heavy coiled spring 2--ain the valve socket b, of sufficient strength to resist the full line pressure in the main valve chamber L and prevent ther relief valve from opening against the spring due to said pressure whenfthe valve is held to its seat by the combined spring pressure and fluid pressure beneath the pis ton Z. The movement of the relief valve is limited by the pin c passing through the transverse aperture al in the valve and secured at each end in the, valve piston Z.

The piston Z is of the differential type and is provided with an enlarged head c forming a pressure area materially greater than the opposing pressure area on the face of the relief valve V` and pressure behind the piston head e will force the relief valve V to its seat U with suicient force to compress the strong spring c and also hold the piston head e firmlyagainst the seat f in the casing extension Y, so that leakage of fluid past the piston from behind the pis'- ton head is shut off and prevented. rl`he relative longitudinal movement or lost motion connection provided between the relief valve V and the piston Z enables both the valve and the piston to be tightly seated on their Aseats U and f respectively.

yA projection or stop g on the piston Z is adapted to bear upon an adjusting screw It in the cap lV, by means of which the initial starting position of the piston Z and relief valve V may be adjusted. A b v-pass y' leads' from themain valve chamber L and communicates with a port opening behind the piston Z and controlled by a set-screw o forming a choking needle valve.

The unloader so far described prevents the fluid compressing load from comin' upon the machine until the motor is up to full speed. Fluid,vas air, enters the main valve casing K at the inlet side and leaves at the discharge outlet O, and the main check valve Q holds back the air in the receiver D and pipe lines while the compressor is idle. When the compressor is started, any slight pressure built up in the main valve chamber L will force bothrthe relief valve V'and the piston Z rearwardly and substantially all the air being pumped will p-ass out through the port X to atmosphere. It is to be assumed that the adjusting lscrew h has been set at such a point that the relief valve and piston move rearwardly and vopen the relief valve the required amount, so that when the compressor is up to full speed, there will be a throttling pressure of a few pounds as the air passes the relief valve. This low pressure is transmitted slowly through the by-pass connection and port c controlled by the choking -needle valve o, behind the differential iston head e, and finally forces the piston Zp and the relief valve V to their seats by the time full compressorspeed is reached. After this int is reached, all the air passes the main ch)O tem.

Greater closing of thechoking set screw or needle valve o delays the loading int but this choking valve should preferab y be as nearly closed as will allow the device to operate for loading. Adjustment ofthe screw h behind the pistonZ determines the pressure to which the side dischar e to atmosphere through port Z will-be built up by relief valve V, by the time the compressor has reached full speed. This adjusting screw h should preferably be set lat a point to produce justl enough throttling at the relief valve V to move the piston Zinwardly and `close the relief valve V when vthe choking needle valve o is set well towards its seat in the port Ic. The throttling due to the Aslightly open relief valve Vl neednot be coni siderable, but should be at least a pound'or two, in order to start buildinup an initial pressure in the receiver tank when startlng;I with the said tank entirely empty.

oading should be delayed until substantially full compressor speed is reached, and unloading should occur automatically just as, or before, the compressor stops entirely. lln order to accomplish unloading on stopping the compressor, means are provided for quickly reducing the pressure behind the head e of the piston Z, which causes the piston to be instantaneously driven rearwardly pfy the pressure in front of the relief valve For this urpose l prefer to connect one or more ble er valves, substantially like the valve disclosed, in my aforesaid Patent No. 1,421,309, between the port q of the unloader eck valve Q to the sys? and the compressor cylinder C, in this instance two such bleeder valves s being so connected to the indicator taps :n at each end of the compressor as by means of the pipes p and y.. The pipe p leads to one end of one portion s of the bleeder valve casing, while the other pipe y connects'to the opposite end of the other portion fw of the bleeder valve casing. 'A diaphragm u is held between the casing portions s and w, and carries a needle valve t oontrolling'the port t', which Vents the pipe p and the space behind the .relief valve piston Z to atmosphere through the bleeder valve atmospheric ports r when pressure beneath the diaphragm u is relieved as the compressor stops. A check valve 2 in the casing portion w having a minute hole 2 is held to its seat by a spring 3,' and the .diaphragm u is subject to the pressure in the compressor, which holds the needle valve t to its seat against thelpressure of a light spring rv during the runnlng period. When the compressor stops, the air under the diaphragm u passes through the-,small hole 2 back into the compressor cylinder, and the needle valve t then opens, thus venting the space back of the relief valve piston Z to atmosphere through the ports r, and permitting the relief valve V and piston Z to be forced rearwardly to open the relief valve V. All the air then in the compressor cylinder and discharge pipe up to the check valve Q is at once relleved to atmosphere through the atmospheric port X, and the'compre/s'sor is unloaded, ready to start.

The unloader should be adjusted to unload as promptly asrpossible onv stopping. The more nearly closed the choking valve o is set, the more prompt will be theunloading, and the setting may be such that the compressor will be completely unloaded during the last few strokes ofthe piston.

l The light spring o is for the purpose of positively aisting the opening of the` bleeder valve t, but is preferably omitted entirely, sinoe the valve will be opened automatically due to the full pressure in the pipe @on the valve and the suction produced in thejcompressor cylinder C at each suction stroke, which at slow speed, just before stopping, is sufficient to drop the valve t. \With out the spring fu, a ver slight pressure in the compressor cylinder sucient for instance to open. its discharge valves, will be enough to close the bleeder valve t immediately after starting the compressor, thus closing any communication between the pipe p and the atmosphere.

By usin two bleeder valves for the compresser cy vinder, the last few suction strokes 'at either end of the air compressing cylinils By this means the operation o the unloader 18e ramener is entirely independent of leakage throu h the discharge valves of the compressor. y connecting bleeder valves to operate/on the slow Suction strokes just before stopping, reduced cylinder pressure .is always assured, and theunloader has been found to operate satisfactorily'and Well in actual practicei l claim:

1. A compressor unloader comprising a valve casing having a main valve chamber adapted to be connected in the discharge line of the compressor, a main discharge valve controlling the outlet from, said chamber to the discharge line, a vent to atmosphere from said chamber, and an automatic differential relief valve controlling said vent to atmosphere and subjected on opposed differential pressure surfaces to the lpressure in the main valve chamber, whereby a delayed time element is produced between the starting of the compressor land the opening of said main discharge valve.

2. A compressor unloader comprising a valve casing having a. main valve chamber adapted to be connected in the discharge line of the compressor, a main discharge valve controlling the outlet from said chamber to .the discharge line, a vent to atmosphere from said chamber, and an automatic differential relief device controlling said vent to atmosphere, consisting of a piston having an enlarged head and a spring pressed relief valve movable on said piston, both the spring pressed relief valve and the piston head being subjected to fluid pressure from the main valve chamber for actuating the piston and valve together and thereby preventing the loading of theJ compressor until an element of time has elapsed after starting.

3. A compressor unloader comprising a valve casing having a main valve chamber adapted. to be connected in the discharge line of the compressor, a main discharge valve cont-rolling the outlet from said chamber to the discharge line, a. vent to atmosphere from said chamber, a relief valve controlling said vent to atmosphere, a piston on which said relief valve has limited longitudinal movement, a spring between the valve and piston, the piston being subject to the pressure eX- isting in the main valve chamber tending to move the relief valve to closed position and hold the valve closed, whereby the load is not thrown on the compressor until the compressor has reached a speed sufficient to build up enough pressure in the said main valve chamber to actuate the piston in a direction to close the said relief valve.

4. A compressor unloader comprising a valve casing having a main valve chamber adapted to be connected to the discharge line of the compressor, a main discharge valve controlling the outlet from said chamber to the discharge line, a vent to atmosphere from said chamber, an automatic relief valve controlling said vent to atmosphere and actuated both to open and close by fluid pressure, thereby preventing the opening of the main discharge valve until the compressor has attained sufficient speed to permit the load to be `safely thrown on the compressor, and means for automatically relieving the pressure holding the relief valve closed as the compressor stops, in order to vent the main valve chamber to atmosphere and unload the compressor on stopping.

5. A compressor unloader comprising a valve casing having a main valve chamber adapted to be connected in the discharge line of the compressor, a main discharge valve controlling the outlet from said chamber to the discharge line, a vent to atmosphere from said chamber, an automatic differential relief valve controlling said vent to atmosphere and subjected on opposed differential pressure surfaces to the pressure in the main valve chamber, whereby a delayed time element is produced between the starting of the compressor and the opening of said main discharge valve, and an automatic bleeder valve controlled by the pressure in the compressor, for automatically relieving the pressure holding the relief valve closed as the compressor stops, in order to vent the main valve chamber to atmosphere and unload the compressor on stopping.

6. A compressor unloader comprising a valve casing having a main valve chamber adapted to be connected in the discharge line of the compressor, a main discharge valve controlling the outlet from said chamber to the discharge line, a vent to atmosphere from said chamber, an automatic di'erential relief device controlling said unit to atmosphere, consisting of a piston having an enlarged head and a spring pressed relief valve movable on said piston, both the spring 'pressed relief valve and the piston head being subjected to luid pressure from the main valve chamber for actuating the piston and valve together and thereby preventing the loading of the compressor until an element \of time has elapsed after. starting, and an automatic bleeder valve controlled by the pressure in the compressor, for automatically relieving the pressure on the enlarged piston head holding the relief valve closed as the compressor stops, in order to vent the main valve chamber to atmosphere and unload the compressor on stopping.

7. A compressor unloader comprising a valve casing having a main valve chamber adapted to be connected in the discharge line of the compressor, a main discharge valve controlling the outlet from said chamber to the discharge line, a vent to atmosphere from said chamber, a relief valve controlling said vent to atmosphere, a piston on which said relief valve has limited longitudinal movement, a spring between the valve and piston,

lthe piston being subject to the pressure eX- isting in the main valve chamber tending to move the relief valve to closed position and hold the valve closed, whereby the load -is not thrown on the compressor until the compressor has reached a speed sufficient-'to build up enough pressure in the said main valve chamber to actuate the piston ina direction to close the said relief valve, and an automatic bleeder valve controlled by the pressure' in the compressor for automaticall relieving the pressure rearwardly of the plston holding the relief valve closed as the compressor stops, in order to vent the main valve chamber to atmosphere and unload the com presser on stopping.

8. A compressor unloader comprising a valve casing having a main valve chamber adapted to be connected in the discharge line of the compressor, a main discharge valve controlling the outlet from said chamber to the discharge line, a vent to atmosphere from said chamber, and an automatic differential relief device cont-rolling said vent to atmoshere, consisting of a piston having an enarged head and a spring pressed relief valve movable on said piston, both the spring pressed relief yvalve and the piston head b e'- ing subjected to fluid pressure from the main valve chamber for actuating the piston and valve together and thereby preventing the loading of the compressor until an element of time has elapsed after starting, and means for throttling the supply of fluid pressure ,from the main valve chamber to 'aetuate the. piston in a direction to close the relief valve.

9. A compressor unloader comprising a valve casing having a main valve chamber adapted to be connected in the discharge line of the compressor, a main discharge valve controlling the outlet from said chamber to the discharge line, a vent to atmosphere from said chamber, a relief valve controlling said vent to atmosphere, a piston on which said relief valve has limited longitudinal movement, a spring between the valve and piston, the piston being subject to the pressure existing in the main valve chamber tending t0 move the relief valve to closed position and hold the valve closed, whereby the load is not thrown on the compressor until the compressor has reached a speed sulicient to build up enough pressure in the said main valve chamber to actuate the piston in a direction .to close the said relief valve, and means for throttling the supply of fluid pressure from the main valve chamber to actuate the piston in a direction to close the relief valve.

lin testimony whereof I have signed this specification.

, SNOWDEN B. REDFIELD. 

